STAT3 and heart failure: Since atrial natriuretic factor (ANF) is known as a marker for heart failure, we examined the mRNA expression level of ANF which was higher expressed in cardiac tissue of infected WT (7.20 ± 3.54 fold, P = 0.0823) and STAT3 KO (5.11 ± 1.18 fold, P = 0.0079) mice as in control animals.